Gobos are used in theatres, TV studios, etc., to set desired light patterns and to project a pattern onto a surface. Gobos are a type of diapositive image placed in powerful projectors for projecting the pattern of the gobo onto a background to provide a light pattern or a light image thereon. In order to enable the light pattern to appear in a non-darkened surrounding, powerful projectors are required, these projectors generating a great deal of heat, partly in the form of IR radiation, meaning that the gobo must be heat-resistant.
Because of the high temperatures that prevail, typical plastic diapositives or transparencies cannot be used and it is necessary to either cut or etch the contours of the patterns in metal sheets or in a metal-coated glass sheet. The most usual method of colouring a pattern at present is to mount a colour filter in front of or behind the pattern. This enables only one colour to be applied, however. A multi-colour picture or image can be produced by this method with the aid of several projectors, each having a colour-part of the image directed on one and the same surface, wherewith the overlapping projections reproduce the basic pattern in colour.
It is known to produce a multi-colour image with the aid of a gobo by building-up a plurality of colour-emitting dichroic coatings on a glass plate. The colour-emitting coatings are built-up one at a time. Each coating corresponds to a colour in the image and consequently it is necessary to re-mask when one coating/colour has been built-up and the build-up of a new coating/colour shall commence. In turn, each coating involves a plurality of thin layers with alternate high and low refractive indexes. The coating is normally applied in a vacuum vapourization chamber. It is necessary to remove the glass plate from the chamber and re-mask between coatings, which is a time-consuming, expensive and irrational process. Furthermore, there is a risk of contamination each time the glass plate is masked or removed from the chamber.